O2 Sensor Heater Problem

[richie00boy]

I have a 2013 Zafira, 1.8 petrol. It's running OK, but there is an engine light on so I checked the code with an OBD reader and Torque app and it reported that the heater on the pre-cat O2 sensor is not working. I have measured the heater resistance at 10.4 ohms which I believe is fine, so I went on the look at the voltages on the heater wires (with the plug disconnected). Across the wires I got nothing. Measuring with respect to earth I got battery voltage on one wire and the other had about 3V on it for about 20 seconds after starting the car then it dropped away to nothing.

I also have an Astra 1.6 petrol so I compared the measurements, on that I get 3.8V at startup and it remained at 3.8V for the minute I was testing.

So I think this must mean that the loom is OK but there is something wrong with the ECU? Or possibly a relay in the circuit with bad contacts?

Also, the battery voltage on the Zafira is higher than I expected - 14.2V. Could this be indicative of an issue or maybe even have damaged something?

 

[tigdlo]

14.2V

You may get a higher than normal reading for a short time after it has been charging, leave it for 30 mins to get a proper measurement. If it has an AGM battery it may charge at a higher voltage, approx 15v I think these were generally fitted to cars with auto stop/start.

Check you meter on another battery and with the car running to see if is reading as expected to rule out the meter reading high.

Not sure about your O2 sensor heater circuit but I would back probe the plug and check the voltage with the O2 sensor plugged in to get a full set of readings before deciding the next step.

Do you have a woring diagram?

 

[richie00boy]

Thanks. It's just a normal battery and I measured 13 ish volts on the Astra which is what I'm used to seeing.

I initially wanted to take measurements with the connector mated, but the thin probes I had poked down the seals couldn't pick anything up.

I don't have a wiring diagram.

 

[rcx132]

An O2 heater issue should be simple to diagnose as it's just a heater? I'm no expert but I would check there's power to the heater pins at the plug. I would potentially repeat this test with a load to be sure there isn't a deeper problem in the wiring. Maybe bench test the heater as well.

I've just wired an engine on my buggy. The O2 sensor was simple with only four wires. Two supply power (ground and positive). One is a sensor ground which is some sort of isolated ground used for sensitive sensors. The other is the O2 signal wire. The only difficult bit to test was the signal as it only generates a signal if the engine is revved for a while. A more modern car like yours might have a wide band sensor which I suspect gives a more consistent signal than my old narrow band sensor.

 

[Keithmac]

Normally the sensor heater "ground" is duty cycle controlled from the PCM.

Just bare that in mind when testing.

The PCM looks at the return voltage though the pulsed ground to deem weather the sensor is functioning or not.

You can put a bulb across the two heater pins in the lambda sensor connector to check heater supply function (and ability to pass current).

The sensor side is normally biased from the PCM, around 3v, when the Lambda is fully heated the sensor brings this voltage down (expect 50mv to 950mv on a functioning narrowband sensor).

Wideband will be 0v to 5v but not common on earlier cars.

 

[richie00boy]

Thanks Keith this is exactly what I was thinking, however I'm still struggling to find how to fix it.
Measuring across the heater wires on the Zafira I get nothing, on the Astra I get about 10V (connector not mated in both cases).
My worry is it's a fault with the ECU.

I'm trying to find some wiring diagrams this morning but it's not easy finding what I need.